Added check in config/.scripts/*.sh scripts wether the needed commands are available

Fixed shebang for some scrips
Removed unnecessary config/.scripts/lock.sh and replaced lock.sh with i3lock.py in the script that executed lock.sh

config/.scripts/screen.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+type xbacklight >/dev/null 2>&1 || { echo >&2 "I require xbacklight but it's not installed.  Aborting."; exit 1; }
+type dunstify >/dev/null 2>&1 || { echo >&2 "I require dunstify but it's not installed.  Aborting."; exit 1; }
 
 case $1 in
     "up"*)